The driving mechanism for a bicycle and the driving mechanism for a leisure recreational pedal boot are identical in principle. Both driving mechanisms comprise a rotational axle, two cranks, or the left and right cranks, and a pair of pedals. More specifically, the two cranks are rendered different in rotational phase by 180°, with one end of each crank being fixed to the rotational axle at a right angle. The other end of each crank is provided with a shaft, which is anchored to the crank at a right angle, and around which a pedal is rotationally fitted. Torque is generated as an operator steps on the pedal, and this torque is used to rotate the propelling means, such as a wheel, a propeller, or the like, of a human-powered vehicle to move the vehicle. In recent years, there have appeared a tricycle and a four-wheel-cycle, in addition to a bicycle, and they seem to have been used even for competitive sports, in Europe and the United States. However, the driving mechanism for a human-powered vehicle has not changed at all in principle.
A bicycle is very widely used as means for recreation, means for commuting to and from school or work, and means for competition, and therefore, the bicycle industry is very large. Here, the present invention will be described with reference to a bicycle for the sake of simplicity.
A bicycle has been developed in accordance with its usage, and therefore, there are many kinds of bicycles different in structure and appearance. As far as the present invention is concerned, which relates to a driving mechanism for a human-powered vehicle, there are bicycles equipped with a speed changing mechanism for improving a bicycle in speed and climbing performance. There are various speed changing mechanisms. Basically, they comprise a plurality of sprockets attached to a follower axle, that is, the rear wheel axle (hereinafter, this type of sprocket will be referred to as “follower axle sprocket”), and only a single sprocket attached to the driving axle by a chain, whereas some of them comprise a plurality of sprockets attached to the driving axle (hereinafter, this type of sprocket will be referred to as “chain ring”), and the aforementioned follower axle sprockets, which are connected to each other by a chain. Also widely used in the field of a human-powered vehicle are driving mechanisms equipped with a planetary gear mechanism attached to the follower axle. It should be noted here that in this patent application, the human-powered vehicle driving mechanism means a driving mechanism for transmitting human power to the speed changing mechanism of a human powered vehicle, or the propelling means, for example, a wheel, a propeller, and the like, of a human-powered vehicle.
In principle, a speed changing mechanism does not improve energy conversion efficiency, regardless of its configuration. In other words, it does not increase the total amount of the power transmitted to a propelling means (bicycle rear wheel, boat propeller, and the like), or reduce the total amount of energy consumed by a driver per hour.
If an attempt is made by a bicycle rider to climb a slope using the same speed increasing ratio as that used when the rider is running on flat land, a □larger force is necessary, and whether or not the rider can continue riding the bicycle is determined by the strength of the legs of the rider. To the rider, a speed changing mechanism is an apparatus for trading the speed of applying force for the applied force, or an apparatus for optimizing the balance between speed of applying force and the applied force. In other words, if the muscular force becomes insufficient upon uphill riding, the speed changing mechanism is down-shifted to reduce the speed increasing ratio, allowing the muscles to move at a higher speed with a smaller amount of force, and yet producing the same amount of power. However, reducing the speed increasing ratio below a certain level is meaningless. That is, as the speed increasing ratio is reduced in order to keep the bicycle running, the rider must pedal faster to rotate the driving axle faster in reverse proportion to the decrease in the speed increasing ratio, which in turn causes the rider to reach his or her limit in physical capacity, and also increases the friction and/or vibrations for which the bearings and chain of the driving mechanism are responsible. Eventually, it becomes impossible for the rider to keep the bicycle balanced to continue riding.
The provision of a speed changing mechanism does not guaranty increase in the power input. Thus, it is obvious that there is a limit in the improvement in slope climbing performance. Therefore, a means for increasing the power input by a rider has been desired. Here, the power input by a rider means the amount of the power (amount of work per unit of time) transmitted from the rider of a bicycle, that is, a human-powered vehicle, to the bicycle through the driving mechanism of the bicycle. In a speed changing mechanism, the revolution of its output shaft is in inverse proportion to the amount of the torque output through the output shaft, the product of the two (revolution of the output shaft and the amount of the torque output through the output shaft) remains constant. In other words, a speed changing mechanism allows the speed increasing ratio, that is, the balance point between the muscular speed and force, to be changed in accordance with the physical capacity of a rider and the riding conditions, in the direction to allow the rider to feel more comfortable. In principle, however, a speed changing mechanism does not change the overall amount of the power input by a rider, and therefore, the overall amount of the power output through the output shaft does not change.
Changing the length of a crank results in a trade-off between the speed at which a rider moves his or her muscles, and the amount of muscular force generated by him or her per pedaling stroke. Optimizing the crank length sometimes results in a small amount of increase in output, but this does not mean increase in input.
There are a certain number of inventions regarding the above described driving mechanism for a human-powered vehicle, for which patent applications have been submitted (U.S. Pat. Nos. 4,125,239, 4,706,516, 4,807,491, and the like). According to them, the cranks of a bicycle are configured so that they can be lengthened or shortened, and the rotational phases of the cranks are synchronized with the lengthening or shortening of the cranks with the use of a planetary gear based mechanism or a cam based mechanism so that the cranks become longest when they are horizontally extending forward to increase the amount of the maximum torque input by the rider.
In the case of the above described driving mechanism for a human-powered vehicle, as one of the pedals moves past the position where the crank to which the pedal is attached is horizontal, it enters a part of its rotational range in which the crank to which the pedal is attached begins to shorten. In this rotational range of the pedal, the force which acts in the radial direction of the locus of the pedal shaft, that is, a component of the force input by the rider through the pedal, drastically increases and resists the shortening of the crank, interfering with the rotation of the crank.
Even in the case of the human-powered vehicle driving mechanism described above, as long as the force applied to a pedal is always made to act tangential to the locus of the pedal shaft, this force does not interfere with the rotation of the crank. Actually, however, the ankle joints, knee joints, and hip joints, are limited in their ranges of movement, and therefore, the force applied to the pedal always acts downward in the virtually vertical direction regardless of rotational angle of the crank. Thus, when a crank is virtually horizontally extending forward, the tangential line to the locus of the pedal shaft and the direction in which the force is applied to the pedal virtually coincide with each other, and therefore, the magnitude of the “torque,” that is, the component of the force applied to the pedal, which acts in the direction to rotate the pedal about the driving axle becomes maximum.
However, as the pedal moves past the point which corresponds to the virtually horizontal forward position of the crank, the torque (more precisely, the force which acts in the rotational direction of the crank, that is, a component force of the resultant force of the gravitational force, inertial force, and muscular force,) reduces, whereas the component force perpendicular to the rotational direction of the crank (more precisely, the force which acts in the longitudinal direction of the crank, that is, a component force of the resultant force of gravitational force, inertial force, and muscular force), that is, the force which acts in the direction to lengthen the crank against the force which acts in the direction to shorten the crank, increases, creating an effect equivalent to the effect of a mechanical brake. Thus, as far as a single rotational cycle of the crank is concerned, this structural arrangement for a human-powered vehicle driving mechanism has not increased power output in practical terms.
As an invention similar to the aforementioned human-powered vehicle driving mechanism, in which the crank length are rendered variable, there is U.S. Pat. No. 4,872,695. According to this patent, the driving mechanism comprises a rear wheel fork, a pair of bearings, a pair of connecting rods, a pair of cranks, and a pair of pedals. The bearing is pivotally attached to the rear wheel fork, and one end of the connecting rod is slidably fitted in the bearing. The end portion of the crank is rotationally connected to the connecting rod, at a point slightly toward the end portion with respect to the center, and the pedal is attached to this end portion of the rod. Thus, as a rider steps on the pedal, the connecting rod acts as a lever having the bearing as its fulcrum, amplifying the applied force from the rider as it is transmitted to the crank.
According to this cited invention, the applied force from the rider is amplified regardless of the rotational angle of the crank, and therefore, the torque definitely increases while the crank is in the portion (hereinafter, down stroke period) of its rotational range in which the pedal moves from its highest position (so-called top dead center) to its lowest position (so-called bottom dead center). However, while the crank is in the portion (hereinafter, up stroke period) of its rotational range in which the pedal moves from its lowest position to its highest position, negative torque is amplified. During the latter period, “leverage” is greater than during the former period; in other words, the ratio at which negative torque is amplified is greater than the ratio at which positive torque is amplified. Thus, as far as the entirety of a single pedaling cycle is concerned, increase in power output cannot be expected even in the case of the structural arrangement disclosed in the cited patent.
FIG. 13 is a graph created by modifying FIG. 7.3 in High-Tech Cycling (Human Kinetics, P.O. Box 5076, Campaign, Ill., USA) in order to effectively describe the present invention, and shows the relationship between the rotational force (the tangential component of the force acting on a pedal) and crank angle. The change of the rotational force while an American bicycle racer was pedaling with a power of 350 W (which appears to represent the amount of work effected upon the crank per unit of time, although no clear definition is given in the above document), at 90 rpm, is plotted on the axis of ordinates, and the crank angle θ (clockwise angle with reference to the top dead center) is plotted on the axis of abscissas. According to this graph, the rotational force is highest when the crank angle θ is slightly greater than 90°, and begin to rapidly reduce as the crank angle θ is beyond approximately 120°.
A fact that the rotational force reduces while the crank angle θ is in a range of 120°<θ<180°, in which a sufficient portion of the combination of the weight of the lower limb and the muscular force, acted on the pedal, indicates that during this period, the combination of the weight of the lower limb and the muscular force acts overwhelmingly in the direction to stretch the crank, instead of the direction to rotate the crank. As a result, the energy of the rider is consumed to stretch the crank which could not be stretched. In other words, no matter how large the force applied to the pedal is, as long as the force is caused to act in the direction to stretch the crank, the amount of work accomplished is zero in terms of dynamics. However, within the body of the rider, blood rapidly circulates, and chemical reactions rapidly occurs, while consuming the energy of the rider. On the other hand, in a range of 217°<θ<345°, the rotational force is negative. This is due to the fact that in a range of 180°<θ<360°, the amount of the muscular force which acts in the direction to forwardly rotate the crank, and the weight of the limb which acts in the direction to reversely rotate the crank, equalized at a crank angle of approximately 200°, and eventually, the latter exceeded the former.
The human-powered vehicle driving mechanism disclosed in Japanese Laid-Open Patent Applications 58-133986, 58-221783, and 8-113180 comprise a pair of, that is, left and right drive trains, driving sub-mechanisms made up of a combination of a rope and pulleys, a combination of reciprocable chain and sprockets, and a rack and a pinion gear, correspondingly. In these driving mechanisms, the left and right drive trains are mechanically connected to each other in such a manner that when one side is in the forward stroke, the other side is in the backward stroke (incidentally, the names used for the above described driving mechanism components were arbitrarily chosen by the inventors of the present invention for convenience in describing the components, and they do not necessarily match the names used in the original specifications). For example, as the pedal of the left drive train is stepped in its forward stroke, the applied force is transmitted to the pulley, sprocket, and pinion gear through the rope, chain, and rack, correspondingly, and therefore, the wheels connected to the pulley, sprocket, and the pinion, correspondingly, rotate. When the left drive train is in the backward stroke, the pedal of the left drive train is lifted by the power from the right drive train. Also during this period, the pulley, sprocket, or pinion gear in the left drive train is allowed to idle relative to the output shaft, by a free wheeling mechanism, such as a rachet or one-way clutch, with which their shaft portions are provided.
Whichever of the above described inventions is used, during the forward stroke, human power acts in the direction tangential to the pulley, sprocket, or pinion gear, and therefore, the entirety of the applied force equals to the rotational force (converts into torque). However, at the end of the forward stroke, the movement of the lower limb is suddenly stopped while moving in the positive direction, and therefore, the kinetic energy of the lower limb, chain, rack, sprocket, pinion gear, and the like is forced to become zero. Thus, in terms of the entirety of each pedaling cycle, a significant amount of increase in output cannot be expected from the driving mechanism in accordance with any of the aforementioned inventions.
Japanese Laid-Open Patent Application 58-199279 discloses an invention, according to which the driving mechanism is rendered reciprocal with the employment of a combination of a chain and a sprocket, and a spring is made to absorb a part of the energy transmitted as a rider steps on a pedal, so that the pedal is returned to the pre-stepping (original) pedal position, by the energy stored in the spring. However, this invention also has a problem in that unless the pedaling motion is not synchronized with the free spring movement, increase in the output cannot be expected (if the pedal is stepped on before it fully returns, a sufficient distance is not available for pedal acceleration to have positive work even in the case of this invention, the initial pedal speed, or the pedal speed at the very moment the pedal begins to be stepped on, is considered to be 0 m/s), and therefore, a significant amount of increase in bicycle speed cannot be expected.
A certain number of studies have been done regarding a human-powered vehicle driving mechanism, which have noted the fact that a muscle generates larger force when it is contracted at a low speed than when it is contracted at a high speed. According to these studies, the chain ring, which normally is truly circular, was made elliptic or the like, and the relationship in the rotational phase between the chain ring and crank was devised to reduce the fluctuation in the crank revolution, so that a rider can apply a larger amount of muscular force to a pedal. However, this method has also a problem in that if the aforementioned relationship in the rotational phase between the chain ring and crank is fixed, the usage of the bicycle is limited. For example, a certain phase difference, which may be suitable for riding a long distance at a constant speed, may not be suitable for riding up a slope or riding at full speed.
The object of the present invention is to solve the problems in the above described prior technologies, so that it becomes possible to provide a driving mechanism which is capable of efficiently converting human power into driving force, and therefore, is most suitable for a human-powered vehicle such as a bicycle, a tricycle, a four-wheel-cycle, a wheelchair, a boat, a human-powered air plane, or a driving mechanism for a device comparable to a human-powered vehicle, for example, a muscle training device.